1. Technical Field
The invention relates to non-aqueous organic electrolytic solution for a lithium primary battery, and a lithium primary battery. Specifically, the invention relates to a technique for modifying non-aqueous organic electrolytic solution included in a lithium primary battery whose cathode active material is manganese dioxide and whose anode active material is lithium or lithium alloy.
2. Related Art
In lithium primary batteries, lithium or lithium alloy is used as an anode active material and manganese dioxide, copper oxide or the like is used as a cathode active material. The lithium primary batteries have a construction in which a positive electrode material containing cathode active material and a negative electrode material containing the anode active material are placed in a cell can with a separator therebetween, and in which the cell can is filled with non-aqueous organic electrolytic solution and is sealed.
The lithium primary batteries, especially those using manganese dioxide as a cathode active material, have high energy density and the following features: it is possible to discharge for long period and the voltage drop is small until the end stage of discharge. The lithium primary batteries are therefore widely used in power supplies of devices such as a stationary gas meter, a stationary water meter and the like, which continue to supply power to the devices for long period. In addition, lithium primary batteries which have not yet been used can be stored for long period. There are various types of lithium primary batteries which are different in the shape of the cell can, positional relationship in the cell can between the positive electrode material and the negative electrode material or the like. The following Non Patent Literature 1 describes the constructions of various lithium primary batteries and the like.
[Non Patent Literature 1] FDK CORPORATION, “Lithium battery”, [online], [search result on Sep. 7, 2013], Internet <URL:http://www.fdk.co.jp/battery/lithium/index.html>
In lithium primary batteries, when a battery is stored at elevated temperatures, decomposition of the electrolytic solution produces gas. The gas increases the pressure in the battery, and leakage may occur in some cases. In lithium primary batteries using manganese dioxide as a cathode active material, when a battery is stored at a deep depth of discharge, the internal resistance increases. More specifically, though a device which operates for long period using lithium primary batteries (e.g. a gas meter and a water meter) gradually loses the capacities of its lithium primary batteries as a result of long-term use, the device operates with almost no problems till the capacities of the lithium primary batteries embedded therein are used up. This is because of their flat discharge characteristics, that is, the voltage drop is small until the end stage of discharge. That is, the device suddenly stops at the time of “dead battery”, in which the capacity is used up. As for a device which has a lithium primary battery as a power source and operates for long period, it is therefore necessary to change its batteries in good time for dead battery. Generally, batteries are replaced periodically before the device will stop due to dead battery.
In some cases, however, a device may stop before the time of battery replacement and may be left for long period because of moving or long-term absence. In this case, the problem that the device cannot be restarted after long-term stop may occur. Whereas lithium primary batteries which have not been used yet have an excellent long-term storability, long-term storage after a battery is once discharged increases the internal resistance. If a device stops at a time near the end of discharge (at a deep depth of discharge), it is therefore impossible to generate a voltage for restarting the device. This makes the device inoperable.